Telephony encompasses the general use of equipment to provide voice communication over a distance. Plain old telephone service, or POTS, is the most basic form of residential and small business telephone service. POTS became available soon after the telephone system was introduced in the late 19th century and, from the standpoint of the user, has existed more or less unchanged ever since. POTS services include bi-directional or full duplex voice path with a limited frequency range, a dial tone and ringing signal, subscriber dialing, operator services such as directory assistance, and long distance and conference calling. During the 1970s and 1980s, new network services became available due to the creation of electronic telephone exchanges and computerization. New services included voice mail, caller identification, call waiting, reminder calls and other similar services.
Advances in digital electronics have revolutionized telephony by providing alternate means of voice communication than those provided by traditional (analog) telephone systems. IP Telephony is a form of telephony which uses the TCP/IP protocol popularized by the Internet to transmit digitized voice data. The routing of voice conversations over the Internet or through other IP networks is also called VoIP (Voice over Internet Protocol). Digital telephony was introduced to improve voice services, but was subsequently found to be very useful in the creation of new network services because it can transfer data quickly over telephone lines. Computer Telephony Integration (CTI) enables a computer to control phone functions such as making and receiving voice, fax, and data calls. The Session Initiation Protocol (SIP) is a signaling protocol used for creating, modifying and terminating sessions (voice or video calls) with one or more participants. Sessions include Internet telephone calls, multimedia distribution and multimedia conferences. Development of the SIP protocol was motivated by the need for a signaling and call setup protocol for IP-based communications that could support the call processing functions and features present in the public switched telephone network (PSTN) using proxy servers and user agents.
Interactive text messaging is a form of real-time communication between two or more people based on typed text. Interactive text messaging differs from email in that text conversations are conducted in real-time using computers connected over a network such as the Internet. A client program on a text messaging user's computer connects to an interactive text messaging service. The user types a message and the service sends the text message to the recipient. Popular interactive text messaging services on the Internet include .NET Messenger Service, AOL Instant Messenger, Excite/Pal, Gadu-Gadu, Google Talk, iChat, ICQ, Jabber, Qnext, QQ, Meetro, Skype, Trillian, Yahoo! Messenger and Rediff Bol Instant Messenger.
All the advances in telephony and interactive text messaging, however, have not solved some very basic problems associated with actually reaching a desired party. Communication in real-time is currently impossible between people who have access only to devices of different modalities. For example, when one user only has access to an ordinary (voice-only) telephone and another only has access to a (text only) Instant Messaging client, there is no way for the two users to communicate in real-time. The below addresses these and other problems.